The present invention relates to apparatus for determining and indicating the position of a movable member, such as a manually adjustable control lever. More particularly, there is disclosed herein apparatus for using radiant energy to detect the position of the movable member.
In the past, it has been common to control the operational characteristics of a controlled device in accordance with the position of a movable member by connecting the movable member to either a linear or rotary potentiometer, whereby movement of the movable member changed the setting of the potentiometer. The signal derived from the wiper arm of the potentiometer was then applied to the controlled device for controlling the operational characteristic of interest. One example of such an application is the fader control commonly employed in audio consoles. In the past, these fader controls have consisted of a linear potentiometer whose settling was controlled by the operator. The voltage signal derived at the wiper arm of the potentiometer was applied to a voltage controlled amplifier (VCA) for controlling its gain.
Potentiometers, however, tend to wear with time, eventually becoming so electrically "noisy", that replacement is required. Further, there is a period of gradual deterioration between the time of first use and the time that replacement is mandated. It would be desirable to provide some manner of controlling the operational characteristic of the controlled device which avoided this operational degradation with time, preferably maintaining quiet operation indefinitely.
Devices have been developed which utilize radiant energy to determine the position of a movable member in order to avoid the mechanical contact inherent in potentiometers and the like. Such devices are described in U.S. Pat. Nos. 3,363,106; 4,100,420; 3,835,384 and others.